The arrangement shown in the figure measures the velocity $$V$$ of a gas of density $$1kg/{m^3}$$ flowing through a pipe. The acceleration due to gravity is $$9.81m/{s^2}.$$ If the manometric fluid is water (density $${1000kg/{m^3}}$$ ) and the velocity $$V$$ is $$20 m/s,$$ the differential head $$h$$ (in $$mm$$) between the two arms of the manometer is ______.

A metal ball of diameter $$60mm$$ is initially at $${220^ \circ }C.$$ The ball is suddenly cooled by an air jet of $${20^ \circ }C.$$ The heat transfer coefficient is $$200\,W/{m^2}.K.$$ The specific heat, thermal conductivity and density of the metal ball are $$400\,\,J/kg.K,\,\,400\,\,W/m.K$$ and $$\,9000\,\,kg/{m^3},$$ respectively. The ball temperature (in $${}^ \circ C$$) after $$90$$ seconds will be approximately.

The heat loss from a fin is $$6W.$$ The effectiveness of the fin are $$3$$ and $$0.75,$$ respectively. The heat loss (in $$W$$) from the fin, keeping the entire fin surface at base temperature, is ___________________

In a counter-flow heat exchanger, water is heated at the rate of $$1.5kg/s$$ from $$\,40{}^ \circ C\,$$ to $$\,80{}^ \circ C\,$$ by an oil entering at $$\,120{}^ \circ C\,$$ and leaving at $$\,60{}^ \circ C\,$$. The specific heats of water and oil are $$4.2kJ/kgK$$ and $$2kJ/kgK,$$ respectively. The overall heat transfer coefficient is $$400\,W/{m^2}K.$$ The required heat transfer surface are (in $${m^2}$$) is